1. Field of the Invention
The present invention relates to a reflection type projector using a reflection type image forming means, and more particularly, to a reflection type projector utilizing all the rays emitted from a light source and then separating the emitted light according to a polarization direction so that the intensity of the light projected onto a screen can be increased.
2. Description of the Related Art
In general, a projector is an apparatus for displaying an image formed by an image forming means by projecting the formed image onto a screen using an additional light source. The projector is usually divided into a projection type projector and a reflection type projector depending on the means for forming the image.
FIG. 1 shows an optical system of a conventional reflection type projector. As shown in the drawing, the reflection type projector includes a light source 10 for emitting light, a color wheel 20 for selectively transmitting a predetermined color, such as red, green or blue color, of an input light, a scrambler 30 for mixing rays of the input light having different degrees of intensity into a uniform beam, a focusing lens 32, a collimating lens 34, a polarization beam splitter 40 for changing a proceeding path of an input light, a display device 50 for forming an image by selectively reflecting an input light, and a projection lens unit 60 for projecting an input light onto a screen (not shown).
The light source 10 is comprised of a lamp 11, such as a metal haloid lamp or a xenon arc lamp, for generating light and a reflecting mirror 13 for reflecting the light emitted from the lamp 11. The color wheel 20 is installed along the optical path of the light between the light source 10 and the scrambler 30 to be capable of being rotated by a driving motor 21. The color wheel 20 is composed of equal areas of red (R), green (G) and blue (B) areas. According to the response speed of the display device 50, any one of the R, G and B areas of the color wheel 20 being rotated is positioned along the optical path of the light. Then, an image is formed as the three colors of R, G and B are overlapped in sequence.
The scrambler 30 mixes rays of the input light by diffusingly-reflecting the same such that the input lights are changed into a uniform light. The focusing lens 32 focuses and diverges the light having passed through the scrambler 30 to enlarge the width of the light transmitted. The collimating lens 34 changes the diverging light into a parallel beam.
The polarization beam splitter 40 is disposed along the optical path of the light between the collimating lens 34 and the display device 50, and changes a proceeding path of an input light by selectively transmitting or reflecting the input light at a mirror surface 41 according to the polarization component thereof. That is, the light proceeding from the side of the light source 10 is selectively transmitted or reflected depending on whether the polarization component of the light is a S-polarization beam or an P-polarization beam.
FIG. 1 shows an example in which light transmitted through the polarization beam splitter 40 is used as an effective light. A ferroelectic liquid crystal display (FLCD) of a two dimensional array structure exhibiting a superior response speed is employed as the display device 50. The display device 50 has a plurality of reflection areas of a two dimensional array structure. The reflection areas, each being independently driven, form an image by modulating the polarization direction of an input light.
The light input to the display device 50 is reflected again and re-enters the polarization beam splitter 40. Here, the beam re-entering the polarization beam splitter 40 has its polarization direction changed by 90.degree. by the display device 50. Then, the beam is totally-reflected by the mirror surface 41 of the polarization beam splitter 40 to proceed toward the projection lens unit 60. The beam passes through the projection lens unit 60 and is projected onto a screen (not shown).
Alternatively, a digital mirror device (DMD) can be provided as the display device 50. The DMD is of a two dimensional array structure and includes a plurality of reflection mirrors each being hinge-coupled to be capable of independently pivoting. Each of the reflection mirrors is selectively driven according to a corresponding pixel of an image to change the angle of reflection of light. In the case that the DMD is employed as the display device 50, the polarization beam splitter 40 is not necessary.
According to the conventional reflection type projector, color of an image is embodied by means of the color wheel 20 disposed along an optical path of the light. That is, an image is displayed by sequentially projecting three colors (R, G and B) onto a screen. Therefore, the intensity of light is lowered because the amount of light is theoretically reduced to 1/3 that of the light originally emitted from the light source, thereby reducing the efficiency of the light.